Conventional reflective designs such as coatings, pigments and paints having varying optical properties of reflectance, transmittance, and absorptance in different wavelength regions are known. Such designs are utilized in a variety of industries, and can be implemented on objects to improve their optical properties. In particular, such designs provide different reflectance and absorptance values for electromagnetic radiation (e.g., solar radiation) depending upon the wavelength of the electromagnetic energy. Solar energy is mostly composed of visible light having a wavelength in the 400 to 700 nm range (hereinafter visible light region) and solar near-infrared light having a wavelength in the 800 to 2500 nm range (hereinafter solar near-infrared region).
In some designs, reflective pigments added to paint products can be utilized on the surface of objects such as buildings or other structures to reduce how much solar energy is absorbed by the surface, converted to heat, and then transmitted into the buildings. This is because the optical properties of the reflective pigments are formulated to increase reflectance values of visible light and/or solar-near-infrared light in comparison to stand alone non-reflective pigment added paint products.
Cool pigments are available commercially as ceramic or organic pigments and are typically used for cool paints that reflect, transmit, and absorb visible and solar near-infrared light with values that differ from conventional pigments. These cool paints absorb less solar near-infrared light and reflect more solar near-infrared light than paints made with conventional colored pigments while providing a range of visual colors. However, because they also transmit solar near-infrared light, cool paints are often painted on opaque white or other highly reflective backgrounds that increase the reflectance of the solar near-infrared light; the white or highly reflective backgrounds reflect the light that is transmitted through the cool paint. However, it is not desirable for many applications to paint dark cool paints on bright, highly reflective backgrounds, because if the cool paint is scratched or disturbed, then the bright background color appears. For example, if a car, painted with a dark cool paint on a white background, was scratched so that the cool paint was removed and the background color was exposed, then the scratch would appear white. This is undesirable since the dark car would then have a white scratch line. Therefore, it would be desirable to develop cool pigments that were opaque, dark colored, had high solar near-infrared reflectance, and did not require white or highly reflective backgrounds, so that they could be used in paints on dark color backgrounds, such as dark primer coatings.
Metallic flake pigments are also well known in the art and are commercially available. However, there are no known designs for cool pigments that use metallic flake pigments that contain specifically designed multilayer coatings. Generally metallic flakes are designed for visual colors only, or for visual colors that change with viewing angle to yield color shifting paints that are used for anti-counterfeiting applications or for decorative paints. Since multilayer thin film coatings can be specifically designed by appropriate selection of coating materials and thicknesses to achieve properties that do not exist in ceramic or organic pigments, it would be advantageous if multilayer thin film coatings could be designed with optical properties appropriate for cool coatings and cool pigments that were superior to existing cool pigments. It would be further advantageous if these multilayer thin film designs did not require bright or white reflective backgrounds for optimized reflectance.
In temperate climates that have buildings receiving considerable amounts of solar energy, it is desirable to reduce the amount of absorbed solar energy that results in additional heating of buildings. This reduction in thermal heating of buildings enables lower energy costs during cooling of such buildings, which is desired. Similar effects are desirable in other objects, such as cars, etc. which are exposed to solar heating and require cooling.
In many of the above described designs, however, there is a problem in that color selection, especially for dark colors, is not available without greatly reducing the solar near-infrared reflectance. Generally, conventional cool color coatings or paints have an average reflectance value in the solar near-infrared region of less than 50%. Ideally, since solar near-infrared energy is responsible for about half of the solar energy that causes thermal heating in structures such as buildings, cars, and roofs, it is desirable to limit how much of this light is absorbed by the structure. In particular, it would be desirable to have an average reflectance that is much greater than 50% in the solar near-infrared light region.
The reflectance of visible light from an object determines the color of that object. Accordingly, it is also desirable to have an average reflectance of a coating, pigment composition, etc. which coats an object in the visible light range such that dark and bright colors can be readily formed without loss of average reflectance in the solar near-infrared region.